Helmet mounted displays provide convenient and quick means for accessing vital flight information, particularly for fighter pilots where reaction time in response to certain stimuli is extremely important. Helmet mounted displays typically include an image source which is mounted on a helmet and projects an image onto a visor also mounted on the helmet. Such displays are described, for example, in U.S. Pat. Nos. 3,923,370 and 4,761,056.
The helmet of a fighter pilot is generally intended to protect his head from dangerous impact in situations such as a crash or circumstances of wind blast arising from a broken canopy. Typical helmets are constructed from a thin lightweight shell and a transparent polycarbonate visor. The helmet shell is relatively flexible to allow for comfortable donning and doffing.
In modern helmet mounted displays, the visor is an optical component whereby an image generated by an optical module is projected onto the visor and reflected towards the pilots eye. Hence, preventing visor deformation is critical for achieving good optical performance. Furthermore, visors used in such helmets are apt to lift upwards under strong wind pressure against the visor, experienced for example, when the aircraft's canopy is ruptured. Needless to say, it is important for visors to remain in place in the face of strong wind pressure.
One method of helmet construction which achieves a stable non-deforming visor uses a rigid shell as an optical platform, where both the visor and an optical module are attached to the shell. The rigidness of the shell prevents any deformations of the visor from arising. However, such a solution makes donning and doffing of the helmet inconvenient. Furthermore, the rigidness of the shell is achieved at the expense of extra, otherwise unnecessary weight that makes the helmet uncomfortable to wear for extended periods of time.